A company managed by former prison officials has been overcharging inmates in most of Japan's prisons for their daily necessities for almost two decades, sources said Monday.

Kyosei Kosaikai has supplied daily goods for inmates to purchase, including underwear and shampoo, to almost all of Japan's 74 correctional facilities based on private contracts.

Many prisoners have complained that goods they have to buy through Kyosei Kosaikai are more expensive than in ordinary supermarkets.

Sales at the prisons total about 200 million yen a year and account for 75 percent of the company's annual turnover, the sources said.

Kyosei Kyokai, a government-affiliated body in charge of ordering these goods from wholesalers, told Kyodo News in a statement, "We are purchasing goods that are as reasonable and proper as possible after getting cost estimates."

"It is indispensable to have this kind of company in order to respond to small orders," said Kazuo Kawano, a director of the association. "There are no problems."

Kyosei Kosaikai, established in 1974, started out as a car insurance company. It began supplying daily goods to prisons in 1986.

Of 19 executives and employees at the company, 18 are former prison officials, the sources said. Some of them are former heads of prisons, they said.

Seiji Horiuchi, president of the company, said Kyosei Kosaikai has provided 14 kinds of daily goods, including underwear, shampoo and electric razors, to almost all prisons in the country, apart from five women's prisons.

These goods are also sold at shops in correctional facilities. Many people who visit prisons buy the goods and give them to prisoners.